In recent years, liquid crystal display apparatuses have been replacing the CRT (Cathode Ray Tube) which has been the mainstream of display apparatuses because of its advantages of lower power consumption, smaller space, lower price, and the like.
The liquid crystal display apparatus is classified to some types by, for example, illuminating methods at the time of displaying an image. A representative liquid crystal display apparatus is a transmission-type liquid crystal display apparatus for displaying an image using a light source disposed at the back of a liquid crystal panel.
In such a display apparatus, it is extremely important to reduce consumption power and to increase display brightness in order to increase the commercial value of the display apparatus. Consequently, it is strongly demanded to increase the gain of an optical system provided between a liquid crystal panel and a light source while suppressing the power consumption of the light source as much as possible.
For example, a technique of providing a prism sheet as a brightness enhancement film between a liquid crystal panel and a light source is disclosed. The prism sheet is obtained by, for example, disposing a plurality of prisms each of an isosceles triangular prism shape having an apex angle of 90 degrees in parallel on a resin film. By using the light condensing effect of the prisms, surface brightness can be increased. Another technique is also disclosed, using prisms in which a refractive index in the extending direction of the prisms and a refractive index in the arrangement direction of the prisms are different from each other, in the prism sheet. In the prism sheet, by performing polarization separation by inclined surfaces of the prisms using interface reflection caused by variations in the critical angles in addition to the light condensing effect of the prisms, the surface brightness can be increased.
The prism sheet having the polarization separating function as described above can be manufactured by, for example, forming a plurality of solid structures on one surface in a sheet containing semi-crystalline or crystalline resin and stretching the sheet on which the solid structures are formed in one direction (refer to Japanese Unexamined Patent Application Publication No. H01-273002 and U.S. Patent Application No. 2006/0138702).
However, the manufacturing methods have problems such that solid structures easily collapse at the time of stretching and it is not easy to obtain a desired structure accurately.
It is therefore desirable to provide an optical sheet including a solid structure having refractive index anisotropy, whose shape hardly collapses and a display apparatus using the optical sheet. It is also desirable to provide a method of manufacturing an optical sheet, capable of accurately forming a solid structure having refractive index anisotropy.